Abstract: A thin film which becomes a membrane is formed over one major surface of a substrate by a plasma deposition process utilizing microwave electron cyclotron resonance. The substrate is then removed, other than a portion of the substrate which remains as a frame, so as to form a membrane structure. A dense and high quality membrane is formed at a low temperature and the internal stress of the membrane controlled by varying the conditions under which the plasma deposition process is carried out and by heat treating the thin film after its formation.

Abstract: An X-ray absorber layer in the form of single layer of high melting point metal such as Ta, W is formed with granular crystal grains on a mask substrate, so that an internal stress of the layer is reduced. A fine pattern is formed from the absorber layer by reactive sputter etching using CBrF.sub.3 gas as an etchant, so that an X-ray absorber pattern is formed on the mask substrate. The X-ray lithography mask thus fabricated has a fine pattern such as submicron pattern with a high degree of pattern contrast and a high dimensional accuracy.